In internal combustion engines, including diesel and gasoline engines, a fuel and air mixture is combusted in combustion cylinders. Reciprocating pistons in the combustion cylinders are moved between top dead center and bottom dead center positions by a crankshaft below the cylinders in a crankcase. As each piston moves toward its top dead center position, it compresses the fuel and air mixture in the combustion chamber above the piston. The compressed mixture combusts and expands, driving the piston downward toward its bottom dead center position.
Combustion in the cylinder releases energy and generates combustion products and by-products, most of which are exhausted from the cylinder into an exhaust system of the engine during the exhaust phase of the combustion cycle. However, some of the combustion products enter into the crankcase by blowing past seal rings around the pistons, and are thus termed “blow-by gases” or simply “blow-by.” Blow-by gases contain contaminants normally found in exhaust gases, such as, for example, hydrocarbons (HC), carbon monoxide (CO), NOx, soot, and unburned or partially burned fuel. In addition, because the crankcase is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor.
As blow-by gases build up in the crankcase, they must be vented to relieve pressure in the crankcase. Some systems vent the blow-by gases directly to the atmosphere. However, the contaminants in blow-by gases are harmful to the environment. Therefore, emissions concerns make direct atmospheric venting a poor option under most, if not all, operating conditions.
Normally aspirated engines have been developed that direct the crankcase gases back to the intake of the engine and mix them with the fuel and air mixture as it flows into the combustion chamber where the contaminants are mostly burned or oxidized during combustion. However, in an engine with forced induction, returning crankcase gases to the intake side of a compressor in a supercharger or turbocharger can result in fouling of the compressor wheel in a relatively short time period. Therefore, crankcase gases must undergo extensive purification before returning them to the intake in a supercharged or turbocharged engine. Further, even with extensive purification, some level of contamination may still exist that may be harmful to the supercharger or turbocharger or various engine components.
Systems have been developed for engines with forced induction that vent the crankcase gases to the atmosphere after the purification process, rather than introducing them back into the engine for further combustion and potentially fouling or otherwise inhibiting the performance of the supercharger or turbocharger. For example, U.S. Pat. No. 6,691,687, issued to Liang et al. on Feb. 17, 2004 (“Liang”), teaches a crankcase blow-by filtration system. In the system of Liang, crankcase gases are purified with a particle and droplet filter. These gases are heated parasitically via heat exchange with some of the main exhaust gases from the engine and also with an electrical heating element. These gases are further treated with a catalytic soot filter before being released to the atmosphere.
While the system of Liang successfully releases purified crankcase gases to the atmosphere, this system is complex. For example, the system of Liang includes multiple purification stages, additional structure for the parasitic heating, an additional energy source for the electrical heating element, and a catalytic filter dedicated to the crankcase gases. Each of these structures is separate from and in addition to the main exhaust path.
The disclosed control system is directed toward improvements and simplification of the system set forth above.